Cold spray method of applying aluminum seal strips

ABSTRACT

A method for applying a seal strip to a surface of a turbine component by accelerating solid particles to a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface, and impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

This invention is generally in the field of gas turbine power generationsystems. More particularly, the present invention is directed to amethod of efficiently producing high quality seal strips on turbinecomponents, such as on bucket dovetails.

Aluminum seal strips are commonly applied to turbine components, such asbucket dovetails, to prevent fluids from passing between joinedcomponents. FIG. 1 illustrates a typical application of the aluminumseal strips 14 to a dovetail 12 of a turbine bucket 10. The aluminumseal strips 14 generally prevent cooling air from leaking past thedovetail 12 when the turbine bucket 10 is attached to the turbine wheel.It should be noted that the precise configurations and locations wherethe aluminum seal strips 14 are applied to a component may vary from onecomponent to another. For example, turbine buckets attached to a turbinewheel close to the combustors will typically have different geometriesthan turbine buckets attached to the turbine wheel further downstreamfrom the combustors.

Aluminum seal strips 14 are typically applied to turbine components byan arc-wire spray coating process. When performing an arc-wire spraycoating process, a pair of electrically conductive wires are melted byan electric current in or adjacent to a spray nozzle. Air issimultaneously fed through the spray nozzle to atomize the moltenmaterial and deposit the material on a substrate surface. The moltenparticles rapidly solidify to form a coating when the particles strikethe substrate surface.

Before the aluminum seal strips 14 are applied to the surfaces ofdovetail 12 by an arc-wire spray coating processes, the turbine bucket10 must first be prepared to receive the spray coating. The preparationof the surface is typically a multi-step process involving (1) acleaning step, (2) a taping or “masking” step, and (3) a grit blastingstep. During the taping step, all surfaces which are not to be coated byaluminum must be covered with masking. Because turbine buckets oftenhave a complex geometry which varies from one bucket to anotherdepending upon where along the turbine wheel the bucket is designed toattach, masking must often be customized for each bucket and appliedcarefully by hand. After the surface is prepared, the coating is sprayedonto the substrate surface and the masking is removed.

Such a seal strip application process often requires a significantamount of man hours and cost to the turbine manufacturer. Furthermore,the spray-coated seal strips are often applied in a non-uniform mannerdue to the imprecise spray pattern produced by the arc-wire spraynozzle. As such, it would be desirable to provide a more time and costefficient method of applying high-quality aluminum seal strips toturbine components.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention comprises a method for applying aseal strip to a surface of a component by accelerating solid particlesto a velocity sufficient to cause the solid particles to plasticallydeform and bond to the surface and each other when impacted on thesurface, and impacting the solid particles on the surface so as to causethe solid particles to deform and bond to the surface and each other toform the seal strip on the surface.

In another aspect, the present invention comprises a method for applyinga seal strip to a surface of a component utilizing a spray coatingapparatus having a deposition nozzle, a powder fluidizing unit, and apressurized gas source. The powder fluidizing unit is configured todisperse solid particles into a carrier gas and the pressurized gassource provides sufficient pressure to accelerate the solid particlesdispersed in the carrier gas through the deposition nozzle at a velocitysufficient to cause the solid particles to plastically deform and bondto the surface and each other when impacted on the surface. The methodfurther comprises accelerating the solid particles through thedeposition nozzle, and impacting the solid particles on the surface soas to cause the solid particles to deform and bond to the surface andeach other to form the seal strip on the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, illustrating a turbine component withaluminum seal strips.

FIG. 2A is a section view, illustrating a seal strip produced by anarc-wire spray coating process.

FIG. 2B is a section view, illustrating a seal strip produced by kineticmetallization.

FIG. 3 is a schematic, illustrating an apparatus for performing methodsof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises methods of efficiently producinghigh-quality seal strips on turbine components. In some embodiments, asillustrated in FIG. 1, the seal strips 14 comprise aluminum and areapplied to surfaces of the dovetail 12 of a turbine bucket 10. Theprecise location and configuration of the seal strips 14 may vary fromone bucket to another, depending upon where on the turbine wheel thebucket is to be installed.

In one aspect, the present invention comprises a method for applying theseal strip 14 to the surface by accelerating solid particles to avelocity sufficient to cause the solid particles to plastically deformand bond to the surface and each other when impacted on the surface, andimpacting the solid particles on the surface so as to cause the solidparticles to deform and bond to the surface and each other to form theseal strip 14 on the surface. This deformation and bonding process,which is an entirely solid-state process, may be referred to as “kineticmetallization”. When undergoing kinetic metallization, the solidparticles experience a very large strain upon collision with the surfacewhich causes the particles to flatten, increasing each particle'ssurface area. Other particles collide and flatten against the previouslyflattened and deposited particles and metallurgical bonds are formedbetween the particles and the surface.

In some embodiments, the solid particles comprise a metal powder, suchas powdered aluminum. The particles may be accelerated to speeds greaterthan about 350 m/sec and impacted upon the surface to deposit thealuminum as a strip on the surface. The solid particles may beaccelerated using a high-pressure gas, such as pressurized helium orair.

It has been discovered that seal strips produced by kineticmetallization have superior properties to seal strips produced byarc-wire spray processes. It has further been discovered thatkinetically-metallized seal strips may be applied more efficiently andwithout surface preparation steps typically required for applying sealstrips by arc-wire spray processes.

FIGS. 2A and 2B are illustrative of seal strips produced by an arc-wirecoating process and a kinetic metallization process, respectively. Asillustrated in FIG. 2A, an arc-wire coated strip 18 possesses anon-uniform and irregular coating pattern. The depth of the coating,measured from the exterior surface of the coating to the surface of thesubstrate 16, varies unpredictably across the width of the strip 18.Also, pockets of entrained air are prolific throughout the coating.These qualities result from air being mixed with the molten materialwhile the material solidifies.

As illustrated in FIG. 2B, the kinetically-metallized strip 20 possessesa more uniform and regular coating pattern compared to the arc-wirecoated strip 18 of FIG. 2A. The coating depth is predictable across thewidth of the strip 18. Also, pockets of entrained air are only sparselypresent throughout the coating. It has been discovered that such acoating pattern produced a superior seal between turbine components.

In another aspect, as illustrated in FIG. 3, the present inventioncomprises a method for applying a seal strip utilizing a spray coatingapparatus 34 having a deposition nozzle 30, a powder fluidizing unit 26,and a pressurized gas source 22. The powder fluidizing unit 26 isconfigured to disperse solid particles into a carrier gas 32. Thepressurized gas source 22 provides sufficient pressure to accelerate thesolid particles dispersed in the carrier gas 32 through the depositionnozzle 30 at a velocity sufficient to cause the solid particles toplastically deform and bond to the surface and each other when impactedon the surface. The solid particles may be fed to the powder fluidizingunit 26 from a hopper 24. The carrier gas 32 may be supplied from thepressurized gas source 22 or a different source. The apparatus 34 mayfurther include a thermal conditioning unit 28 the gas to the desiredoperating temperature.

The method further comprises accelerating the solid particles throughthe deposition nozzle 30, and impacting the solid particles on thesurface so as to cause the solid particles to deform and bond to thesurface and each other to form the seal strip on the surface.

The apparatus 34 is capable of depositing solid particles on a turbinecomponent surface to form a coating substantially as illustrated in FIG.2B. Further, the deposition nozzle 30 may be configured to deposit acoating of a predefined width with excellent edge control (i.e., thecoating produced using the deposition nozzle 30 may have a well-definededge). Such a feature allows apparatus 34 to be used to apply akinetically-metallized seal strip 14 to a turbine component withoutrequiring additional preparation steps, including taping the turbinecomponent with protective masking. Further, the steps of surfacecleaning and grit blasting the surface of the turbine component may beomitted since the solid particles may be bonded to an unprepped surfaceby kinetic metallization.

It should be appreciated that the deposition nozzle 30 may be integratedto a robotic arm to allow a fully-automatic coating process to beperformed. The robotic arm may be controlled by a programmablecontroller which controls actuators or servomechanisms on the roboticarm to direct specific coating configurations at defined locations onthe surface of the turbine component. For example, the robotic arm maybe controlled by any controller adapted for use with CNC machining. Itshould be appreciated that coating depth, width, and length may becontrolled by actuation of the robotic arm. For example, the robotic armmay articulate slowly to deposit a thick coating or quickly to deposit athin coating. Also, the deposition nozzle 30 may be placed in closeproximity to the surface of the turbine component to deposit a striphaving a narrow width or may be placed at a greater distance from thesurface to deposit a strip having a wide width. Furthermore, differentcontrol sequences may be used for each turbine component to allow uniqueseal strip configurations to be applied to various components. Forexample, different control sequences may be used for each turbine bucketto deposit the seal strip in the preferred locations with the preferredconfiguration.

The foregoing robotic system may be designed to operate withcommercially available cold-spray devices. For example, a cold-spraydevice from Supersonic Spray Technologies, a division of CenterLine Ltd.(Detroit, Mich.) may be integrated with a CNC controlled robotic arm andequipped with an appropriate deposition nozzle 30 to carry out theforegoing method. The preferred design of the deposition nozzle 30 is afunction of the operating pressure of the cold-spray device as well asthe desired spray pattern.

The invention is not limited to the specific embodiments disclosedabove. Modifications and variations of the methods and devices describedherein will be obvious to those skilled in the art from the foregoingdetailed description. Such modifications and variations are intended tocome within the scope of the appended claims.

1. A method for applying a seal strip to a component comprising:providing the component having a surface; accelerating solid particlesto a velocity sufficient to cause the solid particles to plasticallydeform and bond to the surface and each other when impacted on thesurface; and impacting the solid particles on the surface so as to causethe solid particles to deform and bond to the surface and each other toform the seal strip on the surface.
 2. The method of claim 1, whereinthe solid particles comprise aluminum.
 3. The method of claim 1, whereinthe solid particles comprise a powdered metal.
 4. The method of claim 1,wherein the component comprises a turbine bucket having a dovetail, andthe surface is located on the dovetail.
 5. The method of claim 1,wherein accelerating the solid particles uses a high-pressure gas. 6.The method of claim 5, wherein the high-pressure gas comprises helium.7. The method of claim 5, wherein the high-pressure gas comprises air.8. The method of claim 1, wherein the velocity is greater than about 350m/sec.
 9. The method of claim 1, further comprising dispersing the solidparticles in a carrier gas before accelerating the solid particles. 10.A method for applying a seal strip to a component comprising: providingthe component having a surface; providing a spray coating apparatuscomprising a deposition nozzle; a powder fluidizing unit; and apressurized gas source; wherein the powder fluidizing unit is configuredto disperse solid particles into a carrier gas and the pressurized gassource provides sufficient pressure to accelerate the solid particlesdispersed in the carrier gas through the deposition nozzle at a velocitysufficient to cause the solid particles to plastically deform and bondto the surface and each other when impacted on the surface; acceleratingthe solid particles through the deposition nozzle; and impacting thesolid particles on the surface so as to cause the solid particles todeform and bond to the surface and each other to form the seal strip onthe surface.
 11. The method of claim 10, wherein the solid particlescomprise aluminum.
 12. The method of claim 10, wherein the solidparticles comprise a powdered metal.
 13. The method of claim 10, whereinthe component comprises a turbine bucket having a dovetail, and thesurface is located on the dovetail.
 14. The method of claim 10, whereinthe solid particles are accelerated using a high-pressure gas.
 15. Themethod of claim 14, wherein the high-pressure gas comprises helium. 16.The method of claim 14, wherein the high-pressure gas comprises air. 17.The method of claim 10, wherein the velocity is greater than about 350m/sec.
 18. The method of claim 10, wherein the deposition nozzle isattached to a robotic arm.
 19. The method of claim 10, wherein thesurface of the component is unmasked.
 20. The method of claim 18,wherein the robotic arm is automatically controlled to deposit the sealstrip on the surface of the component.